Outcast on PC (1999) had Ray Casting (A form of Ray Tracing), Reflections, Open-world. Was a very ground breaking game at the time on the visuals front.
Homeworld 1 (1999) on PC gets a notable mention too... Considering it was released when 3D was just gaining traction in the RTS space, it's held up stupidly well even today... I would even argue that no console at the time can match it visually.
Homeworld was great. Outcast not so much though. Perhaps on today's hardware it looks all right yet when I played it at the time draw distance was very poor and it was quite ugly up close. I much preferred the use of voxels in Comanche maximum overkill